Fluororesin and coated electric wire

ABSTRACT

It is an object of the present invention to provide a fluororesin excellent in thin wall forming ability and capable of forming electric wire insulatings having good flame retardancy, thermal stability and electrical characteristics. The present invention relates to a fluororesin which does not cause cone break, when used for insulating a core wire having a diameter of 0.05 to 0.07 mm under the conditions of a resin temperature of 320 to 370° C., a drawdown rate [DDR] of 80 to 120, a draw rate balance [DRB] of 1.0, a wire coating speed of 700 feet/minute and a insulating thickness of 30 to 50 μm.

TECHNICAL FIELD

This invention relates to a fluororesin and a insulated electric wire.

BACKGROUND ART

Insulated electric wires each composed of a core wire and a insulatingmaterial insulating the same as obtained by molding of a resin arerequired to have a smaller diameter so as to keep up with the recentincreasing trend toward the reduction in size of such articles as mobiledevices. Accordingly, it has become necessary to form a thin insulatingmaterial layer around the core wire with a smaller diameter.

Polyolefin resins such as polyethylene [PE] and polypropylene [PP] havebeen used as resins capable of forming thin-walled layers. However,insulated electric wires manufactured by using the conventionalpolyolefin resins have a problem in that the wall thickness reductionresults in increased transmission losses.

As a result of the advancement of communication technology, insulatedelectric wires are required to be able to transmit large quantities ofinformation. Therefore, it is required that the transmission loss bereduced to a minimum. A method is known for lowering the dielectricconstant and thereby improving the insulating characteristics byinsulating under foaming (cf. e.g. Japanese Kokai Publication H08-7672).However, such foamed insulating materials are insufficient in strengthand, in addition, when the thickness is increased to overcome thatdrawback, a problem arises, namely it becomes difficult to reduce theinsulated wire diameter.

The use of a polyolefin resin as a insulating material presents aproblem from the flame retardancy viewpoint, and a method for overcomingthis problem which comprises adding a flame retardant is known in theart (cf. e.g. Japanese Kokai Publication H07-182930). However, it is aproblem that the addition of a flame retardant results in deteriorationsin electrical characteristics.

A method is known for developing sufficient thermal stability towithstand solder reflow processes which comprises using ageneral-purpose polyolefin resin and curing the same (cf. e.g. JapaneseKokai Publication H06-168627). However, this requires the use of a veryexpensive apparatus and therefore has an economic problem.

Fluororesins, in particular fluororesins comprisingtetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymers [PFAs], areexcellent in thermal stability, flame retardancy and electricalcharacteristics and are used in various fields where theircharacteristics can be displayed. However, PFAs have a problem in thatwhen moldings having minute details or complicated in shape are to beobtained by injection molding, for instance, the moldings tend toundergo surface roughening.

Known as PFA species with which the problem of surface roughening on themolding surface can be solved is a PFA species reduced in molecularweight and having an adjusted molecular weight distribution (cf. e.g.Japanese Kokai Publication 2002-53620). However, when used in insulatingmolding, this PFA produces a problem, namely an increase in insulatingspeed results in worsened thin wall forming ability and in a readytendency toward cone break.

A PFA species further reduced in molecular weight and thus in meltviscosity as well has been investigated as a PFA species with which theproblem of reduced thin wall forming ability on the occasion ofinsulating molding at increased speeds can be resolved. It is a problemof this PFA species, however, that the reduction in molecular weightresults in deteriorations in mechanical characteristics.

DISCLOSURE OF INVENTION Problems which the Invention is to Solve

In view of the above-discussed state of the art, it is an object of thepresent invention to provide a fluororesin excellent in thin wallforming ability and capable of forming electric wire insulatings havinggood flame retardancy, thermal stability and electrical characteristics.

MEANS FOR SOLVING THE PROBLEMS

The present invention relates to a fluororesin which does not cause conebreak, when used for insulating a core wire having a diameter of 0.05 to0.07 mm under the conditions of a resin temperature of 320 to 370° C., adrawdown rate [DDR] of 80 to 120, a draw rate balance [DRB] of 1.0, awire coating speed of 700 feet/minute and a insulating thickness of 30to 50 μm.

The present invention relates to a fluororesin having a critical shearrate, at 360° C., of 200 to 500 sec⁻¹,

wherein the fluororesin mentioned above comprises atetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer and/or atetrafluoroethylene/hexafluoropropylene copolymer.

The present invention relates to a fluororesin whose melt flow rate, at372° C., exceeds 60 (g/10 minutes), wherein the fluororesin mentionedabove comprises a tetrafluoroethylene/perfluoro(alkyl vinyl ether)copolymer and/or a tetrafluoroethylene/hexafluoropropylene copolymer.

The present invention relates to a insulated electric wire comprising acore wire and a insulating material obtained by insulating molding ofthe fluororesin mentioned above for the core wire.

In the following, the present invention is described in detail.

The fluororesin of the invention comprises a melt-processablefluoropolymer containing fluorine atoms directly bound to carbon atoms.

The “melt-processable fluoropolymer” so referred to herein has a meltingpoint within the range of 150-350° C. and a melt viscosity of not higherthan 106 (pascal·sec) as measured at a temperature higher by 50° C. thanthe melting point thereof.

The fluororesin of the invention preferably comprises atetrafluoroethylene-based copolymer [TFE copolymer].

The TFE copolymer is a polymer obtained by copolymerizingtetrafluoroethylene [TFE] and a comonomer other than TFE. The lowerlevel to the content of the comonomer units other than TFE unitsrelative to all the monomer units in the TFE copolymer may be set, forexample, at 1 mole percent, and the upper limit thereto at 30 molepercent, for instance. When the comonomer other than TFE is a PAVE,which is to be mentioned later herein, the lower limit may be 0.01 molepercent and, when the comonomer other than TFE is ethylene, the upperlimit may be lower than 50 mole percent.

The term “all the monomer units” as used herein indicates allmonomer-derived segments constituting the molecular structure of thepolymer.

The “comonomer units other than TFE units” are segments derived from thecomonomer other than TFE as seen from the TFE copolymer molecularstructure viewpoint. Each comonomer unit other than the TFE unit, whenit is a hexafluoropropylene [HFP]-derived one, is represented by—[CF₂—CF(CF₃)]—.

The comonomer other than TFE is not particularly restricted but may be,for example, chlorotrifluoroethylene [CTFE], hexafluoropropylene [HFP],a perfluoro(alkyl vinyl ether) [PAVE] or a like perhalomonomer; Ethylene[Et], vinylidene fluoride [VdF], vinyl fluoride [VF],hexafluoroisobutene, or a hydrogen-containing monomer represented by thegeneral formula (i):CH₂═CX²(CF₂)_(n)X³  (i)wherein X² represents a hydrogen atom or a fluorine atom, x³ representsa hydrogen atom, a fluorine atom or a chlorine atom and n represents aninteger of 1 to 10. Among these, one or a combination of two or more maybe used.

The PAVE mentioned above is not particularly restricted but may be, forexample, perfluoro(methyl vinyl ether) [PMVE], perfluoro(ethyl vinylether), perfluoro(propyl vinyl ether) [PPVE], or perfluoro(butyl vinylether) [PBVE]. Among them, PPVE is preferred from the good thermalstability viewpoint.

The TFE copolymer may be the product obtained by polymerization of theabove-mentioned TFE and comonomer other than TFE and, further, a traceamount monomer. The trace amount monomer may comprise one or acombination of two or more of such comonomers other than TFE asmentioned hereinabove.

The TFE copolymer is not particularly restricted but may be, forexample, a TFE/PAVE copolymer, TFE/HFP copolymer, Et/TFE copolymer,Et/TFE/HFP copolymer or TFE/VdF/HFP copolymer. When, in the presentspecification, a copolymer is specified in terms of monomers, as in thecase of such a copolymer as given above by way of example, the traceamount monomer is sometimes not given in accordance with establishedconvention. It is to be noted, however, that any polymer obtained bycopolymerizing a trace amount monomer in addition to the monomersindicated is not excluded.

The fluororesin of the invention preferably comprises a TFE/PAVEcopolymer, TFE/HFP copolymer and/or Et/TFE copolymer.

The “TFE/PAVE copolymer, TFE/HFP copolymer and/or Et/TFE copolymer” maybe the TFE/PAVE copolymer alone, TFE/HFP copolymer alone or Et/TFEcopolymer alone, or a mixture of two or more copolymers selected fromthe group consisting of the TFE/PAVE copolymer, TFE/HFP copolymer andEt/TFE copolymer.

The above-mentioned mixture of two or more copolymers is generallyproduced by dry blending of two or more copolymers.

The “mixture of two or more copolymers” so referred to hereinconceptually differs from the polymer alloy described later herein inthat said mixture is not one obtained by melt-kneading prior to thestart of insulating molding.

When the fluororesin of the invention comprises a TFE/PAVE copolymer,the perfluoro(alkyl vinyl ether) unit content relative to all monomerunits constituting the TFE/PAVE copolymer is preferably 0.01 to 10 molepercent.

The “perfluoro(alkyl vinyl ether) unit” is the perfluoro(alkyl vinylether)-derived segment in the molecular structure of the TFE copolymer.When the perfluoro(alkyl vinyl ether) unit content is small, the crackresistance of the insulated electric wires tends to lower. As theperfluoro(alkyl vinyl ether) unit content increases, the melt flow rate[MFR] increases and the thin wall forming ability is improved but, onthe other hand, the electrical characteristics tend to deteriorate andthe thermal stability tends to decrease. A more preferred lower limit is0.5 mole percent, a still more preferred lower limit is 1 mole percent,an even more preferred lower limit is 1.9 mole percent, and a mostpreferred lower limit is 2.5 mole percent. A more preferred upper limitis 4.5 mole percent, and a still more preferred upper limit is 4 molepercent.

It has so far been considered that increases in the PAVE content inTFE/PAVE copolymers unfavorably result in melting point lowering and indecreases in thermal stability. The fluororesin of the invention,however, even when it comprises a TFE/PAVE copolymer with a high PAVEcontent, is excellent in mechanical characteristics and in flameretardancy.

The fluororesin of the invention may comprise a polymer alloy obtainedby using two or more copolymers selected from the group consisting ofTFE/PAVE copolymers, TFE/HFP copolymers and Et/TFE copolymers.

The “polymer alloy”, so referred to herein, is obtained by melt-kneadingtwo or more polymer species prior to the start of insulating molding.The polymer alloy may be one resulting from complete mutual dissolutionon the polymer chain level, or one resulting from chemical bondingbetween two or more polymers, or one resulting from formation, in apolymer matrix, of a domain or domains comprising a polymer(s) otherthan the matrix-constituting polymer(s). The size of the domain(s) ispreferably not greater than 1 μm, more preferably not greater than 100nm, per 30 μm of the polymer matrix.

When the fluororesin of the invention comprises such a polymer alloy asmentioned above, the copolymer combination includes TFE/HFPcopolymer-Et/TFE copolymer, TFE/HFP copolymer-TFE/PAVE copolymer, Et/TFEcopolymer-TFE/PAVE copolymer, and TFE/HFP copolymer-Et/TFEcopolymer-TFE/PAVE copolymer combinations and, among them, TFE/HFPcopolymer-TFE/PAVE copolymer combinations are more preferred.

When the fluororesin of the invention comprises such a TFE/HFPcopolymer-TFE/PAVE copolymer polymer alloy as mentioned above and is tobe used in an application field where heat resistance is required, forexample in a solder reflow process, it is preferred that a TFE/PAVEcopolymer be used as a base polymer and a TFE/HFP copolymer be addedthereto, with the proportion of the TFE/HFP copolymer to the totalweight of the polymer alloy being 3 to 40% by weight. A more preferredlower limit is 5% by weight, and a more preferred upper limit is 25% byweight.

Further, when the fluororesin of the invention is a polymer alloycomprising a TFE/PAVE copolymer and a TFE/HFP copolymer, the PAVE unitcontent in the polymer alloy is preferably 0.1 to 4 mole percentrelative to the sum total of 100 mole percent, namely the sum total ofthe TFE, PAVE and HFP units constituting the whole polymer alloy.

The fluororesin of the invention may comprise the above-mentionedpolymer alloy alone, or the above-mentioned mixture of two or morecopolymers and the above-mentioned polymer alloy, or the above-mentionedpolymer alloy in combination with a TFE/PAVE copolymer alone, a TFE/HFPcopolymer alone or an Et/TFE copolymer alone in the sense that it is notthe above-mentioned mixture of two or more copolymers.

In producing the above-mentioned TFE copolymer by polymerization, suchknown methods of polymerization as emulsion polymerization, suspensionpolymerization, solution polymerization and bulk polymerization can beused. From the industrial viewpoint, however, the use of suspensionpolymerization or emulsion polymerization is preferred.

The fluororesin of the invention may further contain a filler. Thefiller is not particularly restricted but includes, among others, flameretardants such as antimony oxide and calcium phosphate; coke, silica,alumina, titanium oxide, zinc oxide, magnesium oxide, magnesiumhydroxide, tin oxide, calcium carbonate, magnesium carbonate, glass,talc, mica, isinglass, boron nitride and aluminum nitride.

The fluororesin of the invention may contain such a flame retardant asmentioned above. However, said fluororesin in itself has a sufficientlevel of flame retardancy without addition of such flame retardant,hence can be free from influences of the addition of a flame retardantsuch as decreases in tensile break strength, decreases in crackresistance, and deteriorations in electrical characteristics.

The fluororesin of the invention preferably has a dielectric constant of1.8 to 2.7. A more preferred upper limit is 2.6, and a still morepreferred upper limit is 2.2.

The fluororesin of the invention preferably has a dielectric losstangent of not greater than 60×10⁻⁴ as measured at 2.45 GHz, forinstance. A more preferred upper limit is 10×10⁻⁴, and a still morepreferred upper limit is 5×10⁻⁴. Within the above-mentioned range of thedielectric loss tangent, the lower limit may be set at 0.5×10⁻⁴, forinstance.

The above-mentioned dielectric constant and dielectric loss tangent arethe values obtained by carrying out measurements by the cavity resonatoroscillation method. The fluororesin of the invention can be renderedexcellent in electrical characteristics such that the dielectricconstant and dielectric loss tangent may be within the respective rangesgiven above.

From the electrical characteristics viewpoint, the fluororesin of theinvention preferably comprises a perfluoropolymer with all carbon-boundhydrogen atoms having been substituted by fluorine atoms.

When the fluororesin of the invention comprises a TFE/PAVE copolymer,the dielectric constant thereof is preferably not greater than 2.2 fromthe electrical characteristics viewpoint, and the perfluoro(alkyl vinylether) unit contents relative to all the monomer units in the TFE/PAVEcopolymer is preferably not lower than 0.1 mole percent, more preferablynot lower than 0.5 mole percent, still more preferably not lower than 1mole percent.

The fluororesin of the invention is high in flame retardancy, asmentioned hereinabove, and has an oxygen index generally exceeding 30,preferably an oxygen index of 90 or higher.

The above-mentioned oxygen index is the value measured in accordancewith ASTM D 2863.

Generally, when the oxygen index is 25 to 27 or higher, the resin, evenupon temporally exposure to fire under ordinary conditions of use as theinsulating material constituting insulated electric wires, will notcontinue burning owing to its self-extinguishing properties.

The fluororesin of the invention may also have a critical shear rate at360° C. of not lower than 200 (sec⁻¹).

Within the above range, the upper limit to the critical shear rate maybe set at 500 (sec⁻¹), for instance. For increasing the insulating speedand thin wall forming ability in insulating molding, a more preferredlower limit is 220 (sec⁻¹).

The fluororesin of the invention preferably has a melt flow rate [MFR]of not lower than 48 (g/10 minutes). A more preferred lower limit to theMFR is 50 (g/10 minutes), a still more preferred lower limit is 60 (g/10minutes) or above, an even more preferred lower limit is 62 (g/10minutes) and a most preferred lower limit is 63 (g/10 minutes). A higherMFR makes it possible to increase the insulating speed when the resin isused in insulating molding, render the resin excellent in thin wallforming ability and improve the insulating material obtained in surfacesmoothness and crack resistance. Within the above range, the upper limitto the MFR can be set at 100 (g/10 minutes), for instance; from themechanical strength viewpoint, however, the upper limit is preferablyset at 85 (g/10 minutes), more preferably 81 (g/10 minutes).

The above-mentioned MFR is the value obtained by measurement under theconditions of a temperature of 372° C. and a load of 5.0 kg inaccordance with ASTM D 1238.

As mentioned above, the fluororesin of the invention has a high MFR anda large number of active terminal groups at polymer chain termini and isadvantageous in that the adhesion to core wires is improved. From theelectrical characteristics improvement viewpoint, however, it is notdesirable that the number of active terminal groups is too large.Therefore, the polymer chain termini may be subjected to fluorinationtreatment to an extent such that the desired electrical characteristicsmay be acquired. The fluorination treatment may be carried out in theconventional manner, for example by exposure to fluorine gas or heatingin the presence of water.

The fluororesin of the invention preferably has a molecular weightdistribution [Mw/Mn] within the range of 1 to 2. When the molecularweight distribution is within the above range, the resin, when used ininsulating molding, can give insulatings improved in surface smoothness.A preferred upper limit to the molecular weight distribution [Mw/Mn] is1.8.

The above-mentioned Mw/Mn is the value measured by the method describedin Polym. Eng. Sci., 29 (1989), 645 (W. H. Tuminello).

The Mw/Mn measurement temperature is 330° C., and the method of dataprocessing and the parameters are as described in the document citedabove.

The fluororesin of the invention, when used in insulating a core wirewith a diameter of 0.05 to 0.07 mm under the conditions of a resintemperature of 320 to 370° C., a wire coating speed of 700 feet/minute,a drawdown ratio [DDR] of 80 to 120, a draw ratio balance [DRB] of 1.0and a insulating thickness of 30 to 50 μm (hereinafter, such conditionssometimes referred to as “specified insulating conditions”), will notcause cone break. If cone break occurs under the specified insulatingconditions mentioned above, the insulated wire made of the core wire anda insulating material obtained by insulating molding of the resin aroundthe core wire on the occasion of molding for insulating the core wirewill become insufficient in insulating properties.

The phrase “not cause cone break” as used herein means that when avoltage of 6 kV is applied to the insulated wire obtained for a periodof at least 0.15 second in accordance with JIS C 3005 using a directcurrent spark tester (hereinafter, such conditions sometimes referred toas “cone break detecting conditions”), the number of sparks per 1000 mis zero. When the fluororesin of the invention is used under theabove-mentioned specified insulating conditions, the number of sparksper 1200 m can be rendered zero and, preferably, the number of sparksper 1500 m can be rendered zero, as evaluated under the above-mentionedcone break detecting conditions.

The resin temperature mentioned above is the temperature of thefluororesin of the invention at the cylinder tip. It is the valueobtained by inserting a spring type fixed thermocouple (product of ToyoDennetsu) into the cylinder inside and measuring the temperature there.When the resin temperature is excessively high, the insulated wireobtained may show cracking or foaming in some instances and, when it isexcessively low, the insulated wire obtained may be poor in surfacesmoothness in some cases. A preferred lower limit to the resintemperature is 330° C., a more preferred lower limit is 340° C., apreferred upper limit is 360° C. and a more preferred upper limit is355° C.

The insulating thickness mentioned above is the thickness of theinsulating obtained after cooling to ordinary temperature of 20 to 30°C. following melt extrusion insulating with the fluororesin of theinvention by insulating molding. The “insulating thickness of 30 to 50μm” mentioned above refers to insulating under conditions such that theinsulating thickness amounts to 30 to 50 μm.

Even when the upper limit to the insulating thickness is preferably setat 45 μm, more preferably at 40 μm, still more preferably at 35 μm, thefluororesin of the invention, when used in insulating under theabove-mentioned specified insulating conditions, can be one causing nocone break.

The insulating thickness mentioned above is the value calculated bydividing by 2 the value obtained by subtracting the outside diametervalue of the core wire measured in advance from the outside diametervalue of the insulated wire as measured by means of Laser Micro DiaMeter (product of Takikawa Engineering). The fluororesin of theinvention, even in the case of insulating under the above-mentionedspecified insulating conditions, makes it possible to molding thin wallshaving such a insulating thickness as mentioned above, without causingcone break.

When a TFE/PAVE copolymer or TFE/HFP copolymer is used as thefluororesin of the invention, the value of the above-mentioned DDR isselected within the range of 80 to 120, and a preferred lower limitthereto is 96, and a preferred upper limit is 104 and the value of theDDR may be set at 100. When an Et/TFE copolymer is used as thefluororesin of the invention, the value of the DDR mentioned above isselected within the range of 30 to 70, and a preferred lower limit is40, a preferred upper limit is 65, and the value of the DDR may be setat 60.

The “DDR” so referred to herein is the value obtained by calculatingaccording to the formula:DDR=(D _(d) ² −D _(t) ²)/(d _(c) ² −d _(b) ²)wherein D_(d) represents the die opening diameter, D_(t) represents thechip outside diameter, d_(c) represents the insulated wire outsidediameter and d_(b) represents the core wire outside diameter.

As for the DRB mentioned above, the tolerance zone is 0.9 to 1.1. Whenthe DRB exceeds 1.1, cone break occurs readily and, when it is below0.9, the insulating material hardly acquires a basically circular crosssection but tends to easily acquire an elliptic section; hence, thevalue of 1.0 is generally selected.

The “DRB” so referred to herein is the value obtained by calculatingaccording to the following formula:DRB=(D _(d) /d _(c))/(D _(t) /d _(b))wherein D_(d), D_(t), d_(c) and d_(b) are as defined above.

Even when the core wire has a diameter of not greater than 0.13 mm, thefluororesin of the invention can be such one that will not cause conebreak when used in insulating under the above-mentioned specifiedinsulating conditions. However, a preferred diameter is 0.05-0.11 mmand, even when the upper limit to the diameter is more preferably set at0.08 mm, still more preferably at 0.07 mm, the fluororesin can be suchone that will not cause cone break. As the core wire diameter decreases,the curvature of the wire surface increases; thus, when attempts aremade to use the conventional resins in molding for insulating fine corewires, the resins show poor “spreading” on the core wires, producing theproblem of cone break. On the contrary, the fluororesin of the inventionwill not cause cone break under the above-mentioned specified insulatingconditions even if the core wire diameter is as small as 0.07 mm orsmaller.

The core wire diameter mentioned above may be the value obtained bymeasurement using a carpenter's square or the value according to theAmerican Wire Gauge [AWG] standard.

For checking for cone break, an electrically conductive wire is used asthe above-mentioned core wire. It may be made of copper, aluminum orsteel, for instance; preferably, copper is used. That the core wire hasa diameter of 0.05 to 0.13 mm corresponds to the fact that the diameteris 44 to 36 as expressed in terms of the American Wire Gauge [AWG]; thatthe diameter is 0.11 mm corresponds to the fact that it is 37 to 38 asexpressed according to the AWG; and that it is 0.07 mm corresponds tothe fact that it is 41 to 42 according to the AWG.

The fluororesin of the invention is more preferably such one that willnot cause cone break when a core wire having a diameter of 0.05 mm isinsulated therewith under the conditions of a resin temperature of 320°C., a wire coating speed of 700 feet/minute, a DDR of 120, a DRB of 1.0and a insulating thickness of 30 μm.

The fluororesin of the invention, when it comprises a TFE/PAVE copolymerwith a perfluoro(alkyl vinyl ether) unit content of 6 to 10 mole percentrelative to all the monomer units, is preferably such one that will notcause cone break upon insulating of a core wire having a diameter of0.05 mm therewith under the conditions of a resin temperature of 320°C., a wire coating speed of 700 feet/minute, a DDR of 120, a DRB of 1.0and a insulating thickness of 30 μm. When it comprises a TFE/PAVEcopolymer with a perfluoro(alkyl vinyl ether) unit content of 1.9 to 4.5mole percent relative to all the monomer units, it is preferably suchone that will not cause cone break upon insulating of a core wire havinga diameter of 0.05 mm therewith under the conditions of a resintemperature of 340° C., a wire coating speed of 700 feet/minute, a DDRof 120, a DRB of 1.0 and a insulating thickness of 30 μm.

The fluororesin of the invention will not cause cone break even whenused in insulating under the above-mentioned insulating conditions, asmentioned above, and therefore is suited for insulated wire productionand is particularly suited for electric wire insulating in view of itsexcellent electrical characteristics.

A fluororesin comprising a TFE/PAVE copolymer and/or TFE/HFP copolymerand having a critical shear rate, at 360° C., of not lower than 200(sec⁻¹) is hereinafter sometimes referred to as “fluororesin (A)”.

For the fluororesin (A), the upper limit to the above-mentioned criticalshear rate can be set at 500 (sec⁻¹), for instance, within the aboverange and, from the viewpoint of insulating speed increasing and goodthin wall forming ability on the occasion of use thereof in insulatingmolding, a more preferred lower limit is 220 (sec⁻¹).

The “critical shear rate” so referred to herein is the shear rate at thetime of arrival at such a state that the fluororesin is allowed to flowout at a temperature of 360° C. through an orifice with a diameter of 1mm and a length of 16 mm under a specific shear stress using acapillograph (product of Bohlin Instruments) begins to undergo meltfracture.

The melt fracture is a phenomenon of the extrudate becoming spiral,indefinite or discontinuous in shape or showing a sharkskin-like surfacewhen the shear rate is excessively high on the occasion of extrusion ofa viscoelastic body through a hole or slit. The occurrence or absence ofmelt fracture can be confirmed, for example, by using a microscope ormagnifying glass at a magnification of 16.

The fluororesin (A) can be such one that the MFR thereof at 372° C. ishigher than 60 (g/10 minutes).

A fluororesin comprising a TFE/PAVE copolymer and/or TFE/HFP copolymerand having an MFR at 372° C. of higher than 60 (g/10 minutes) ishereinafter sometimes referred to as “fluororesin (B)”.

The fluororesin (B) has such a very high MFR as falling within the rangementioned above and, therefore, well enables the insulating speed to beincreased and is particularly excellent in thin wall forming ability, sothat the insulating material obtained can be further improved in surfacesmoothness and crack resistance.

The TFE/PAVE copolymer as a TFE copolymer constituting the fluororesin(A) or fluororesin (B) preferably has a PAVE unit content, relative toall the monomer units in the TFE/PAVE copolymer, of 1.9 to 4.5 molepercent. A more preferred lower limit to that content is 2 mole percent,a still more preferred lower limit is 2.5 mole percent, and a morepreferred upper limit is 4 mole percent. When that resin is a polymeralloy comprising a TFE/PAVE copolymer and a TFE/HFP copolymer, the PAVEunit content in the polymer alloy is preferably 0.1 to 4 mole percentrelative to the total sum, which is taken as 100 mole percent, of theTFE, PAVE and HFP units constituting the polymer alloy as a whole.

When it comprises a TFE/PAVE copolymer, the fluororesin (A) andfluororesin (B) shows almost no lowering either in melting starttemperature or in melting point and displays excellent thermal stabilityin spite of the PAVE unit content being relatively high. Such excellentthermal stability is considered to be an effect of polymer formulation;no probable cause is known, however.

In the present specification, the TFE/PAVE copolymer constituting thefluororesin (A) or fluororesin (B) may be one derived from TFE and aPAVE alone or a copolymer derived from TFE and a PAVE and, further, atrace amount monomer copolymerizable with TFE and the PAVE.

In the present specification, the TFE/HFP copolymer among the TFEcopolymers constituting the fluororesin (A) or fluororesin (B) may beone derived from TFE and HFP alone or a copolymer derived from TFE andHFP and, further, a trace amount monomer copolymerizable with TFE andHFP.

The trace amount monomer in the TFE/PAVE copolymer or TFE/HFP copolymeras the TFE copolymer constituting the fluororesin (A) or fluororesin (B)preferably amounts to 0.1 to 1.5 mole percent relative to all themonomer units in said TFE copolymer.

In the present specification, the TFE copolymer derived from TFE, HFPand a PAVE is referred to as “TFE/HFP copolymer” when the HFP unitcontent is higher than the PAVE unit content upon comparison between theHFP unit content and PAVE unit content relative to all the monomer unitsin the TFE copolymer or is referred to as “TFE/PAVE copolymer” when thePAVE unit content is higher than the HFP unit content.

A more preferred lower limit to the MFR, at 372° C., of the fluororesin(A) or fluororesin (B) is 63 (g/10 minutes).

The upper limit to the MFR, at 372° C., of the fluororesin (A) andfluororesin (B) may be set, for example, at 100 (g/10 minutes) withinthe range mentioned above. From the mechanical strength viewpoint,however, the upper limit is preferably set at 85 (g/10 minutes), morepreferably at 81 (g/10 minutes).

The fluororesin (A) and fluororesin (B) both are excellent in increasinginsulating speed and thin wall forming ability, so that, generally, theynever cause cone break under the cone break detecting conditionsmentioned above and provide electrical characteristics and flameretardancy within the same ranges as mentioned hereinabove.

Preferred as the TFE copolymer constituting the fluororesin (A) andfluororesin (B) are TFE/PAVE copolymers and, in the case of TFE/PAVEcopolymers, excellent mechanical characteristics can be provided inspite of the MRF being as high as within the above range and, further,in the case of those TFE/PAVE copolymers in which the PAVE unit contentrelative to all the monomer units therein is 2.5 to 4 mole percent,still better mechanical characteristics can be provided and the MITfolding endurance, for example, can amount to at least 4000 cycles.

For determining the above-mentioned MIT folding endurance, films(thickness 220 μm×width 13 mm) prepared by using the fluororesin inquestion are subjected to measurements using a folding tester (productof Yasuda-Seiki-Seisakusho) in accordance with ASTM D 2176.

The “fluororesin” simply so referred to herein without adding (A) or (B)conceptually includes not only the fluororesin (A) and fluororesin (B)but also all other fluororesins falling within the scope of the presentinvention.

The fluororesin of the invention is preferably a fluororesin forelectric wire insulating.

The insulated electric wire of the invention comprises a core wire and ainsulating material obtained by molding the fluororesin of the inventionso as to insulate the core wire.

The insulated electric wire of the invention has a insulating formedfrom the fluororesin of the invention as the insulating material and,therefore, can have sufficient thermal stability to endure solder reflowprocesses.

The insulated electric wire of the invention can be produced with easeby using the fluororesin of the invention as the insulating material, asmentioned above, even when the core wire has a diameter of 0.13 mm orsmaller. A preferred upper limit to the core wire diameter is 0.08 mmand a more preferred upper limit is 0.07 mm. The insulated electric wireof the invention preferably has a core wire diameter of not smaller than0.02 mm.

As the core wire material, there may be mentioned copper, aluminum andsteel, among others, and, from the viewpoint of adhesion to theinsulating material, copper is preferred.

The insulating material preferably has a thickness of 10 to 60 μm. Amore preferred lower limit is 15 μm, a still more preferred lower limitis 20 μm, a more preferred upper limit is 55 μm, and a still morepreferred upper limit is 50 μm.

The insulating material thickness mentioned above is the value aftercooling to ordinary temperature, namely 20 to 30° C. followinginsulating.

The insulating material of the insulated electric wire of the inventioncan have such a thin wall thickness as mentioned above, and the crackresistance of the insulating material can be improved.

The above-mentioned insulating material thickness is the value obtainedby dividing, by 2, the value resulting from subtraction of the core wireoutside diameter measured in advance from the outside diameter of theinsulated electric wire as measured using Laser Micro Dia Meter (productof Takikawa Engineering), like the insulating thickness mentionedhereinabove under the specific insulating conditions.

The insulated electric wire of the invention is suitably used as acoaxial cable. The coaxial cable can be a small-diameter coaxial cableas well and can also cope with the reduction in size of mobile devicessuch as cellular phones, for instance. In the case of folding typecellular phones, there are restrictions as to the structure of theirfolding portion; a thick layer is required for strength improvement and,on the other hand, a thin wall is required. The insulated electric wireof the invention can be adequately used under such circumstances.

The insulated electric wire of the invention can also be suitably usedas an image sending wire in a video microscope for medical use.

EFFECTS OF THE INVENTION

The fluororesin of the invention, which has the constitution describedabove, is excellent in thin wall forming ability and can form anelectric wire insulating material having good flame retardancy, thermalstability and electrical characteristics.

BEST MODES FOR CARRYING OUT THE INVENTION

The following examples illustrate the present invention morespecifically. These examples are, however, by no means limitative of thescope of the invention.

SYNTHESIS EXAMPLE 1 Synthesis of Fluororesin F-1

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 0.95 kg of perfluoro(propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 4.5 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.065-kg portions, at1-hour intervals. The polymerization was continued in this manner for 28hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-1 in pellet form.

SYNTHESIS EXAMPLE 2 Synthesis of Fluororesin F-2

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 1.98 kg of PPVE and 4.0 kg of methanol, and thesystem inside temperature was maintained at 35° C. and the rate ofstirring at 200 rpm. Then, TFE was fed under pressure until arrival at0.6 MPa, followed by charging of 0.06 kg of a 50% methanol solution ofdi-n-propyl peroxydicarbonate to initiate the polymerization. Sinceotherwise the system inside pressure would decrease as the progress ofthe polymerization, TFE was continuously fed to maintain the pressurewhile PPVE was added, in 0.117-kg portions, at 1-hour intervals. Thepolymerization was continued in this manner for 28 hours. After pressurerelease to atmospheric pressure, the reaction product obtained waswashed with water and dried to give 30 kg of a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-2 in pellet form.

SYNTHESIS EXAMPLE 3 Synthesis of Fluororesin F-3

A 174-liter autoclave was charged with 43 L of distilled water and,after sufficient nitrogen substitution, further charged with 43 kg ofhexafluoropropylene [HFP], 0.42 kg of PPVE and 0.45 kg of methanol, andthe system inside temperature was maintained at 25.5° C. and the rate ofstirring at 200 rpm. Then, tetrafluoroethylene [TFE] was fed underpressure until arrival at 0.83 MPa, followed by charging of 1.8 kg of a8% (by weight) solution of the polymerization initiator (H(CF₂CF₂)₃COO)₂in perfluorocyclohexane to initiate the polymerization. Since otherwisethe system inside pressure would decrease as the progress of thepolymerization, TFE was continuously fed to maintain the system insidepressure at 0.83 MPa. During polymerization, the 8% (by weight) solutionof (H(CF₂CF₂)₃COO)₂ in perfluorocyclohexane was added, in 0.15-kgportions, at 2-hour intervals until the lapse of 6 hours after the startof polymerization and, then, in 0.13-kg portions, at 2.5-hour intervalsuntil the completion of polymerization. At 1.5 hours after the start ofpolymerization, 0.45 kg of methanol was added and, then, methanol wasadded, in 0.45-kg portions, at 10-hour intervals. PPVE was added, in0.12-kg portions, at 8-hour intervals (0.36 kg in total). Thepolymerization was continued in this manner for 35 hours. After pressurerelease to atmospheric pressure, the reaction product obtained waswashed with water and dried to give 50 kg of a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-3 in pellet form.

SYNTHESIS EXAMPLE 4 Synthesis of Fluororesin F-4

A 174-liter autoclave was charged with 43 L of distilled water and,after sufficient nitrogen substitution, further charged with 43 kg ofHFP and 0.55 kg of methanol, and the system inside temperature wasmaintained at 25.5° C. and the rate of stirring at 200 rpm. Then, TFEwas fed under pressure until arrival at 0.83 MPa, followed by chargingof 0.54 kg of a 8% (by weight) solution of the polymerization initiator(H(CF₂CF₂)₃COO)₂ in perfluorocyclohexane to initiate the polymerization.Since otherwise the system inside pressure would decrease as theprogress of the polymerization, TFE was continuously fed to maintain thesystem inside pressure at 0.83 MPa. During polymerization, the 8% (byweight) solution of (H(CF₂CF₂)₃COO)₂ in perfluorocyclohexane was added,in 0.10-kg portions, at 2-hour intervals until the lapse of 6 hoursafter the start of polymerization and, then, in 0.08-kg portions, at2.5-hour intervals until the completion of polymerization. At 1.5 hoursafter the start of polymerization, 0.55 kg of methanol was added and,then, methanol was added, in 0.55-kg portions, at 10-hour intervals. Thepolymerization was continued in this manner for 37 hours. After pressurerelease to atmospheric pressure, the reaction product obtained waswashed with water and dried to give 55 kg of a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-4 in pellet form.

SYNTHESIS EXAMPLE 5 Synthesis of Fluororesin F-5

A 174-liter autoclave was charged with 43 L of distilled water and,after sufficient nitrogen substitution, further charged with 43 kg ofHFP and 0.24 kg of methanol, and the system inside temperature wasmaintained at 25.5° C. and the rate of stirring at 200 rpm. Then, TFEwas fed under pressure until arrival at 0.83 MPa, followed by chargingof 0.54 kg of a 8% (by weight) solution of the polymerization initiator(H(CF₂CF₂)₃COO)₂ in perfluorocyclohexane to initiate the polymerization.Since otherwise the system inside pressure would decrease as theprogress of the polymerization, TFE was continuously fed to maintain thesystem inside pressure at 0.83 MPa. During polymerization, the 8% (byweight) solution of (H(CF₂CF₂)₃COO)₂ in perfluorocyclohexane was added,in 0.10-kg portions, at 2-hour intervals until the lapse of 6 hoursafter the start of polymerization and, then, in 0.08-kg portions, at2.5-hour intervals until the completion of polymerization. At 1.5 hoursafter the start of polymerization, 0.24 kg of methanol was added and,then, methanol was added, in 0.24-kg portions, at 10-hour intervals. Thepolymerization was continued in this manner for 37 hours. After pressurerelease to atmospheric pressure, the reaction product obtained waswashed with water and dried to give 55 kg of a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-5 in pellet form.

SYNTHESIS EXAMPLE 6 Synthesis of Fluororesin F-6

A 14-kg portion of the powder of Synthesis Example 1 was dry-blendedwith 1.1 kg of the powder of Synthesis Example 5 using a Henschel mixer,and the mixture was pelletized under the melt-kneading and pelletheating conditions shown in Table 1 to give fluororesin F-6 in pelletform.

SYNTHESIS EXAMPLE 7 Synthesis of Fluororesin F-7

A 14-kg portion of the powder of Synthesis Example 1 was dry-blendedwith 2.9 kg of the powder of Synthesis Example 5 using a Henschel mixer,and the mixture was pelletized under the melt-kneading and pelletheating conditions shown in Table 1 to give fluororesin F-7 in pelletform.

SYNTHESIS EXAMPLE 8 Synthesis of Fluororesin F-8

A 174-liter autoclave was charged with 47 L of distilled water and,after sufficient nitrogen substitution, further charged with 33.9 kg ofperfluorocyclobutane, 5.5 kg of HFP, 0.91 kg of PPVE and 5.0 kg ofmethanol, and the system inside temperature was maintained at 35° C. andthe rate of stirring at 200 rpm. Then, TFE was fed under pressure untilarrival at 0.75 MPa, followed by charging of 0.18 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.026-kg portions, at1-hour intervals. The polymerization was continued in this manner for 28hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-8 in pellet form.

SYNTHESIS EXAMPLE 9 Synthesis of Fluororesin F-9

A 174-liter autoclave was charged with 27 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 1.4 kg of PPVE and 1.0 kg of methanol, and thesystem inside temperature was maintained at 35° C. and the rate ofstirring at 200 rpm. Then, TFE was fed under pressure until arrival at0.6 MPa, followed by charging of 0.03 kg of a 50% methanol solution ofdi-n-propyl peroxydicarbonate to initiate the polymerization. Sinceotherwise the system inside pressure would decrease as the progress ofthe polymerization, TFE was continuously fed to maintain the pressurewhile PPVE was added, in 0.065-kg portions, at 1-hour intervals. Thepolymerization was continued in this manner for 28 hours. After pressurerelease to atmospheric pressure, the reaction product obtained waswashed with water and dried to give 30 kg of a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-9 in pellet form.

SYNTHESIS EXAMPLE 10 Synthesis of Fluororesin F-10

A 14-kg portion of the powder of Synthesis Example 4 was dry-blendedwith 1.6 kg of the powder of Synthesis Example 9 using a Henschel mixer,and the mixture was pelletized under the melt-kneading and pelletheating conditions shown in Table 1 to give fluororesin F-10 in pelletform.

SYNTHESIS EXAMPLE 11 Synthesis of Fluororesin F-11

A 174-liter autoclave was charged with 51 L of distilled water and,after sufficient nitrogen substitution, further charged with 32 kg ofperfluorocyclobutane, 0.25 kg of cyclohexane and 0.34 kg of2,3,3,4,4,5,5-heptafluoro-1-pentene (CH₂═CFCF₂CF₂CF₂H), and the systeminside temperature was maintained at 20° C. and the rate of stirring at200 rpm. Then, tetrafluoroethylene was fed under pressure until arrivalat 0.67 MPa and, further, ethylene [Et] was fed under pressure untilarrival at 0.86 MPa. The system inside temperature was then raised to35° C., the system inside pressure was raised to 1.2 MPa and 0.18 kg ofa 50% methanol solution of di-n-propyl peroxydicarbonate was added toinitiate the polymerization. Since otherwise the system inside pressurewould decrease as the progress of the polymerization, a gas composed ofTFE and Et in a mole ratio of 55:45 was continuously fed to maintain thesystem inside pressure at 1.2 MPa. The polymerization was continued inthis manner for 45 hours. After pressure release to atmosphericpressure, water was removed. Then, 51 L of distilled water was added,0.61 kg of a 28% (by weight) aqueous ammonia was added, the systeminside temperature was raised to 80° C., and the mixture was stirred at200 rpm for 3 hours. After pressure release to atmospheric pressure, thereaction product obtained was washed with water and dried to give 25 kgof a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-11 in pellet form.

SYNTHESIS EXAMPLE 12 Synthesis of Fluororesin F-12

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 1.42 kg of perfluoro (propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 3.0 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.072-kg portions, at1-hour intervals. The polymerization was continued in this manner for 26hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-12 in pellet form.

SYNTHESIS EXAMPLE 13 Synthesis of Fluororesin F-13

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 1.42 kg of perfluoro(propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 3.2 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.072-kg portions, at1-hour intervals. The polymerization was continued in this manner for 25hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-13 in pellet form.

SYNTHESIS EXAMPLE 14 Synthesis of Fluororesin F-14

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 1.42 kg of perfluoro(propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 3.6 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.072-kg portions, at1-hour intervals. The polymerization was continued in this manner for 26hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-14 in pellet form.

SYNTHESIS EXAMPLE 15 Synthesis of Fluororesin F-15

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 1.60 kg of perfluoro(propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 3.6 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.080-kg portions, at1-hour intervals. The polymerization was continued in this manner for 26hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-15 in pellet form.

SYNTHESIS EXAMPLE 16 Synthesis of Fluororesin F-16

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 0.84 kg of perfluoro(propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 4.6 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.052-kg portions, at1-hour intervals. The polymerization was continued in this manner for 23hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-16 in pellet form.

SYNTHESIS EXAMPLE 17 Synthesis of Fluororesin F-17

A 174-liter autoclave was charged with 34 L of distilled water and,after sufficient nitrogen substitution, further charged with 30.4 kg ofperfluorocyclobutane, 0.84 kg of perfluoro(propyl vinyl ether)(CF₂═CFOCF₂CF₂CF₃) [PPVE] and 3.5 kg of methanol, and the system insidetemperature was maintained at 35° C. and the rate of stirring at 200rpm. Then, tetrafluoroethylene [TFE] was fed under pressure untilarrival at 0.6 MPa, followed by charging of 0.06 kg of a 50% methanolsolution of di-n-propyl peroxydicarbonate to initiate thepolymerization. Since otherwise the system inside pressure woulddecrease as the progress of the polymerization, TFE was continuously fedto maintain the pressure while PPVE was added, in 0.052-kg portions, at1-hour intervals. The polymerization was continued in this manner for 23hours. After pressure release to atmospheric pressure, the reactionproduct obtained was washed with water and dried to give 30 kg of apowder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-17 in pellet form.

SYNTHESIS EXAMPLE 18 Synthesis of Fluororesin F-18

A 174-liter autoclave was charged with 43 L of distilled water and,after sufficient nitrogen substitution, further charged with 43 kg ofhexafluoropropylene [HFP], 1.15 kg of PPVE and 0.85 kg of methanol, andthe system inside temperature was maintained at 25.5° C. and the rate ofstirring at 200 rpm. Then, TFE was fed under pressure until arrival at0.83 MPa, followed by charging of 1.8 kg of a 8% (by weight) solution ofthe polymerization initiator (H(CF₂CF₂)₃COO)₂ in perfluorocyclohexane toinitiate the polymerization. Since otherwise the system inside pressurewould decrease as the progress of the polymerization, TFE wascontinuously fed to maintain the system inside pressure at 0.83 MPa.During polymerization, the 8% (by weight) solution of (H(CF₂CF₂)₃COO)₂in perfluorocyclohexane was added, in 0.15-kg portions, at 2-hourintervals until the lapse of 6 hours after the start of polymerizationand, then, in 0.13-kg portions, at 2.5-hour intervals until thecompletion of polymerization. At 1.5 hours after the start ofpolymerization, 0.85 kg of methanol was added and, then, methanol wasadded, in 0.85-kg portions, at 10-hour intervals. PPVE was added, in0.25 kg portions, at 8-hour intervals (0.75 kg in total). Thepolymerization was continued in this manner for 35 hours. After pressurerelease to atmospheric pressure, the reaction product obtained waswashed with water and dried to give 50 kg of a powder.

This powder was pelletized under the melt-kneading and pellet heatingconditions shown in Table 1 to give fluororesin F-18 in pellet form.TABLE 1 Melt-kneading and extruxion conditions Pellet heating conditionsC1 C2 C3 C4 AD D Number of screw Temperature Time [° C.] [° C.] [° C.][° C.] [° C.] [° C.] revolutions [rpm] [° C.] [hr] Synthesis 320 340 340340 345 345 15 200 8 Example 1 Synthesis 310 340 340 340 345 345 15 2008 Example 2 Synthesis 290 330 340 340 345 340 15 150 24 Example 3Synthesis 280 320 340 340 340 340 15 150 24 Example 4 Synthesis 290 330340 340 345 345 15 150 24 Example 5 Synthesis 320 340 340 340 345 345 15200 8 Example 6 Synthesis 320 340 340 340 345 340 15 200 8 Example 7Synthesis 320 340 340 340 345 340 15 200 8 Example 8 Synthesis 330 340350 350 360 350 15 200 8 Example 9 Synthesis 280 320 340 340 340 340 15150 24 Example 10 Synthesis 250 265 265 275 280 280 25 150 8 Example 11Synthesis 320 340 340 340 345 340 15 200 8 Example 12 Synthesis 320 340340 340 345 340 15 200 8 Example 13 Synthesis 320 340 340 340 345 340 15200 8 Example 14 Synthesis 310 340 340 340 345 340 15 200 8 Example 15Synthesis 320 340 340 340 345 340 15 200 8 Example 16 Synthesis 320 340340 340 345 340 15 200 8 Example 17 Synthesis 280 320 340 340 345 340 15150 24 Example 18

In Table 1, C1, C2, C3 and C4 respectively indicate fourtemperature-measuring sites on the cylinder. The temperature-measuringsites are positioned in that order at even intervals, C1 being remotestfrom and C4 being closest to the injection hole. In Table 1, AD denotesthe adapter temperature, and D denotes the die temperature.

The fluororesins obtained in the synthesis examples were evaluated forthe following physical characteristics.

(1) Fluororesin Composition Determination

The composition of each fluororesin was determined by ¹⁹F NMR analysis.

(2) Melting Point (Tm) Determination

Using a Seiko model differential scanning calorimeter [DSC], the meltingpeak appearing upon raising the temperature at a rate of 10° C./minutewas recorded, and the temperature corresponding to the maximum wasreported as the melting point (Tm).

(3) Melt Flow Rate [MFR] Measurement of Each Fluororesin

Using a melt indexer (product of Toyo Seiki Seisakusho), the weight (g)of the polymer forced through a nozzle having a diameter of 2 mm and alength of 8 mm in unit time (10 minutes) under a load of 5 kg wasmeasured at the measurement temperature indicated.

The results are shown in Table 2. TABLE 2 MFR[g/10 minute] CompositionMelting (measurement Resin species [mole ratio] point[° C.] temperature)Synthesis Fluororesin TFE/PPVE = 300 63 Example 1 F-1 98.0/2.0 (372° C.)Synthesis Fluororesin TFE/PPVE = 297 67 Example 2 F-2 96.5/3.5 (372° C.)Synthesis Fluororesin TFE/HFP/ 270 36 Example 3 F-3 PPVE = (372° C.)92.7/6.9/0.4 Synthesis Fluororesin TFE/HFP = 265 48 Example 4 F-492.0/8.0 (372° C.) Synthesis Fluororesin TFE/HFP = 265 6 Example 5 F-592.0/8.0 (372° C.) Synthesis Fluororesin TFE/HFP/ 296 45 Example 6 F-6(= F-1 + PPVE = (372° C.) F-5) 97.7/0.6/1.7 Synthesis FluororesinTFE/HFP/ 293 39 Example 7 F-7 (= F-1 + PPVE = (372° C.) F-5)97.2/1.4/1.4 Synthesis Fluororesin TFE/HFP/ 300 49 Example 8 F-8 PPVE =(372° C.) 98.1/1.1/0.8 Synthesis Fluoraresin TFE/PPVE = 300 8 Example 9F-9 98.0/2.0 (372° C.) Synthesis Fluororesin TFE/HFP/ 269 40 Example 10F-10 (= F-4 + PPVE = (372° C.) F-9) 92.6/7.2/0.2 Synthesis FluororesinTFE/Et/ 257 35 Example 11 F-11 H2P = (297° C.) 54.1/43.4/2.5 SynthesisFluororesin TFE/PPVE = 300 63 Example 12 F-12 97.4/2.6 (372° C.)Synthesis Fluororesin TFE/PPVE = 300 67 Example 13 F-13 97.4/2.6 (372°C.) Synthesis Fluororesin TFE/PPVE = 300 77 Example 14 F-14 97.4/2.6(372° C.) Synthesis Fluororesin TFE/PPVE = 300 90 Example 15 F-1597.1/2.9 (372° C.) Synthesis Fluororesin TFE/PPVE = 301 63 Example 16F-16 98.4/1.6 (372° C.) Synthesis Fluororesin TFE/PPVE = 301 46 Example17 F-17 98.4/1.6 (372° C.) Synthesis Fluororesin TFE/HFP/ 265 70 Example18 F-18 PPVE = (372° C.) 92.0/6.9/1.1

EXAMPLE 1

Using the fluororesin F-1 prepared in Synthesis Example 1, insulatingmolding was performed with a copper wire (0.07 mm in diameter) as thecore wire under the molding conditions shown in Table 3.

The dielectric constant, dielectric loss tangent and oxygen index weremeasured by the methods given below. The measurement results are shownin Table 4.

(4) Measurements of Dielectric Constant and Dielectric Loss Tangent ofEach Fluororesin

Measurements were made using a cavity resonator oscillation apparatus(product of Kanto Denshi Oyo Kaihatsu (KEAD)). The measurement frequencywas 2.45 GHz, and the sample subjected to measurements had the shape ofa square bar, 1.8 mm×1.8 mm×130 mm.

(5) Oxygen Index

The method of ASTM D 2863 was followed.

EXAMPLE 2

Using the fluororesin F-2 prepared in Synthesis Example 2, a insulatingmaterial was produced under the same extrusion conditions as in Example1, and evaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 3

Using the fluororesin F-3 prepared in Synthesis Example 3, a insulatingmaterial was produced under the same extrusion conditions as in Example1, and evaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 4

Using the fluororesin F-4 prepared in Synthesis Example 4, a insulatingmaterial was produced under the same extrusion conditions as in Example1, and evaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 5

Using the fluororesin F-6 prepared in Synthesis Example 6, a insulatingmaterial was produced under the same extrusion conditions as in Example1, and evaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 6

Using the fluororesin F-7 prepared in Synthesis Example 7, a insulatingmaterial was produced under the same extrusion conditions as in Example1, and evaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 7

Using the fluororesin F-8 prepared in Synthesis Example 8, a insulatingmaterial was produced under the same extrusion conditions as in Example1, and evaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 8

Using the fluororesin F-10 prepared in Synthesis Example 10, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 9

Using the fluororesin F-11 prepared in Synthesis Example 11, ainsulating material was produced under the same extrusion conditions asin Example 1 except that the extrusion speed was 3.5 (g/minute), andevaluations were made by the same evaluation methods as used inExample 1. The results are shown in Table 4.

EXAMPLE 10

Using the fluororesin F-12 prepared in Synthesis Example 12, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 11

Using the fluororesin F-13 prepared in Synthesis Example 13, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 12

Using the fluororesin F-14 prepared in Synthesis Example 14, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 13

Using the fluororesin F-15 prepared in Synthesis Example 15, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 14

Using the fluororesin F-16 prepared in Synthesis Example 16, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 15

Using the fluororesin F-17 prepared in Synthesis Example 17, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

EXAMPLE 16

Using the fluororesin F-18 prepared in Synthesis Example 18, ainsulating material was produced under the same extrusion conditions asin Example 1, and evaluations were made by the same evaluation methodsas used in Example 1. The results are shown in Table 4.

COMPARATIVE EXAMPLE 1

Low-density polyethylene (50% by weight; Mirason 3530, density: 0.925g/cm³, MFR: 0.25 (g/10 minutes), product of Du Pont-MitsuiPolychemicals) and magnesium hydroxide (50% by weight) were formulatedand mixed up, and the mixture was used for insulating molding under thetemperature and extrusion conditions shown in Table 3. Then, evaluationswere performed by the same evaluation methods as used in Example 1. Theresults are shown in Table 4.

COMPARATIVE EXAMPLE 2

High-density polyethylene (50% by weight; Hizex 7500 M, density: 0.957g/cm³, MFR: 0.03 (g/10 minutes), product of Sumitomo-Mitsui Polyolefins)and magnesium hydroxide (50% by weight) were formulated and mixed up,and the mixture was used for insulating molding under the temperatureand extrusion conditions shown in Table 3. Then, evaluations wereperformed by the same evaluation methods as used in Example 1. Theresults are shown in Table 4. TABLE 3 Exam- Exam- Exam- Exam- Exam-Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam- Exam-Comparative Comparative ple 1 ple 2 ple 3 ple 4 ple 5 ple 6 ple 7 ple 8ple 9 ple 10 ple 11 ple 12 ple 13 ple 14 ple 15 ple 16 Example 1 Example2 Resin species Fluoro- Fluoro- Fluoro- Fluoro- Fluoro- Fluoro- Fluoro-Fluoro- Fluoro- Fluoro- Fluoro- Fluoro- Fluoro- Fluoro- Fluoro- Fluoro-Low-density High-density resin resin resin resin resin resin resin resinresin resin resin resin resin resin resin resin polyethylenepolyethylene F-1 F-2 F-3 F-4 F-6 F-7 F-8 F-10 F-11 F-12 F-13 F-14 F-15F-16 F-17 F-18 (F-1 + F-5) (F-1 + (F-4 + F-5) F-9 Melt- C1[° C.] 300 300280 280 300 300 300 280 280 300 300 300 300 300 300 280 180 180 kneadingC2[° C.] 330 330 330 320 330 330 330 320 300 330 330 330 330 330 330 320200 200 temperature C3[° C.] 340 340 340 340 340 340 340 340 300 340 340340 340 340 340 340 210 210 conditions C4[° C.] 350 350 350 350 350 350350 350 310 350 350 350 350 350 350 350 230 230 C5[° C.] 350 350 350 350350 350 350 350 320 350 350 350 350 350 350 350 250 250 AD[° C.] 350 350350 350 350 350 350 350 320 350 350 350 350 350 350 350 245 245 D[° C.]350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 245 245Resin 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350 350245 245 temperature [° C.] Extrusion Extrusion 4.2 4.2 4.2 4.2 4.2 4.24.2 4.2 3.5 4.2 4.2 4.2 4.2 4.2 4.2 4.2 1.9 2.0 conditions speed[g/minute] Core wire 0.07 diameter [mmφ] Wire coating 700 speed[feet/minute] Insulating 30 thickness [μm] Extruder Cylinder 35 diameter[mm] Screw L/D 24 ratio [−] Screw CR 3 Die Inside 1.3/0.7 diameter/tipoutside diameter [mm/mm] Condition of core No core break Cone breakinsulating occurred

In Table 3, C1, C2, C3, C4 and C5 respectively indicate fivetemperature-measuring sites on the cylinder. The temperature-measuringsites are positioned in that order at even intervals, C1 being remotestfrom and C4 being closest to the injection hole. In Table 3, AD denotesthe adapter temperature, and D denotes the die temperature. TABLE 4Dielectric Dielectric loss tangent Oxygen Resin species constant (× 10⁴)index Example 1 Fluororesin 2.1 4 96 F-1 Example 2 Fluororesin 2.1 4 95F-2 Example 3 Fluororesin 2.1 5 95 F-3 Example 4 Fluororesin 2.1 5 94F-4 Example 5 Fluororesin 2.1 4 95 F-6 (= F-1 + F-5) Example 6Fluororesin 2.1 4 95 F-7 (= F-1 + F-5) Example 7 Fluororesin 2.1 4 95F-8 Example 8 Fluororesin 2.1 5 96 F-10 (= F-4 + F-9) Example 9Fluororesin 2.6 50 31 F-11 Example 10 Fluororesin 2.1 4 96 F-12 Example11 Fluororesin 2.1 4 96 F-13 Example 12 Fluororesin 2.1 5 96 F-14Example 13 Fluororesin 2.1 6 96 F-15 Example 14 Fluororesin 2.1 5 96F-16 Example 15 Fluororesin 2.1 4 95 F-17 Example 16 Fluororesin 2.1 495 F-18 Comparative Low-density 2.9 1500 30 Example 1 polyethyleneComparative High-density 2.9 1500 30 Example 2 polyethylene

From Table 4, it was revealed that the insulating materials molded inExamples 1 to 16 were lower in dielectric constant and dielectric losstangent than the insulating materials molded in Comparative Examples 1and 2. In particular, the insulating materials molded in Examples 1 to 8and 10 to 16 in which the fluororesin comprised a TFE/PAVE copolymer,TFE/HFP copolymer or TFE/HFP/PPVE copolymer or a polymer alloy composedof a TFE/PAVE copolymer and a TFE/HFP copolymer were particularly low indielectric constant and dielectric loss tangent and, further, they werehigh in oxygen index and thus found to be excellent in flame retardancy.

EXAMPLES 17 TO 24

The fluororesins specified in Table 5 were measured for MFR by themethod described above under (3) and also measured for critical shearrate and MIT by the following evaluation methods.

(6) Critical Shear Rate Measurement of Fluororesins

Using a capillograph (product of Bohlin Instruments), each fluororesinwas forced through an orifice having a diameter of 1 mm and a length of16 mm under a varying shear stress at 360° C. and the shear rate (sec⁻¹)at which the fluororesin began to show melt fracture was recorded. Theobservation of the polymer surface for detecting melt fracture was madeunder a microscope at a magnification of 16.

(7) MIT Folding Endurance Measurement

Using a folding tester (product of Yasuda-Seiki-Seisakusho), themeasurement was carried out according to ASTM D 2176 at room temperatureunder a load of 1.25 kg; the folding angle was ±1350. The test specimenswere prepared by molding each fluororesin into a 220-μm-thick film andpunching out 13-mm-wide strips therefrom.

The results are shown in Table 5. TABLE 5 Melting MFR [g/10 minute]Composition point (measurement Critical shear rate MIT Resin species[mole ratio] [° C.] temperature) (sec⁻¹) (cycle) Example 17 FluororesinTFE/PPVE = 300 63 240 4100 F-1 98.0/2.0 (372° C.) Example 18 FluororesinTFE/PPVE = 297 67 240 17000 F-2 96.5/3.5 (372° C.) Example 19Fluororesin TFE/PPVE = 300 63 240 6500 F-12 97.4/2.6 (372° C.) Example20 Fluororesin TFE/PPVE = 300 67 240 6000 F-13 97.4/2.6 (372° C.)Example 21 Fluororesin TFE/PPVE = 300 77 250 5500 F-14 97.4/2.6 (372°C.) Example 22 Fluororesin TFE/PPVE = 300 90 290 5400 F-15 97.1/2.9(372° C.) Example 23 Fluororesin TFE/PPVE = 301 63 240 1500 F-1698.4/1.6 (372° C.) Example 24 Fluororesin TFE/PPVE = 301 46 135 3900F-17 98.4/1.6 (372° C.)

Comparison of Examples 17 and 19 with Example 23 revealed that TFE/PAVEcopolymers with a PPVE unit content of 1.9 mole percent or higher aresuperior in MIT value in spite of little difference in MFR. Inparticular, it was found that TFE/PAVE copolymers with a PPVE unitcontent of 2.5 mole percent or higher are far superior in MIT value.Comparison between Example 17 and Example 24 revealed that TFE/PAVEcopolymers with a PPVE content of 1.9 mole percent or higher can retaintheir high MIT values in spite of their high MFR values.

INDUSTRIAL APPLICABILITY

The fluororesin of the invention is suitably used, for example, as ainsulating material for small-diameter electric wires which is requiredto have high electrical insulating properties and thin-wall formingability.

1. A fluororesin which does not cause cone break, when used forinsulating a core wire having a diameter of 0.05 to 0.07 mm under theconditions of a resin temperature of 320 to 370° C., a drawdown rate[DDR] of 80 to 120, a draw rate balance [DRB] of 1.0, a wire coatingspeed of 700 feet/minute and a insulating thickness of 30 to 50 μm. 2.The fluororesin according to claim 1 which comprises atetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer, atetrafluoroethylene/hexafluoropropylene copolymer and/or anethylene/tetrafluoroethylene copolymer, and/or a polymer alloy obtainedby using at least two copolymers selected from the group consisting of atetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer, atetrafluoroethylene/hexafluoropropylene copolymer and anethylene/tetrafluoroethylene copolymer.
 3. A fluororesin having acritical shear rate, at 360° C., of 200 to 500 sec⁻¹, wherein saidfluororesin comprises a tetrafluoroethylene/perfluoro(alkyl vinyl ether)copolymer and/or a tetrafluoroethylene/hexafluoropropylene copolymer. 4.The fluororesin according to claim 3, whose melt flow rate, at 372° C.,exceeds 60 (g/10 minutes).
 5. A fluororesin whose melt flow rate, at372° C., exceeds 60 (g/10 minutes), wherein said fluororesin comprises atetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer and/or atetrafluoroethylene/hexafluoropropylene copolymer.
 6. The fluororesinaccording to claim 2, wherein the tetrafluoroethylene/perfluoro(alkylvinyl ether) copolymer has a perfluoro(alkyl vinyl ether) unit contentof 1.9 to 4.5 mole percent relative to all the monomer units.
 7. Thefluororesin according to claim 1, which is a fluororesin for electricwire insulating.
 8. A insulated electric wire comprising a core wire anda insulating material obtained by insulating molding of the fluororesinaccording to claim 1, for said core wire.
 9. The insulated electric wireaccording to claim 8, wherein the core wire has a diameter of 0.02 to0.13 mm.
 10. The insulated electric wire according to claim 8, whereinthe insulating material has a thickness of 10 to 60 μm.
 11. Thefluororesin according to claim 3, wherein thetetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer has aperfluoro(alkyl vinyl ether) unit content of 1.9 to 4.5 mole percentrelative to all the monomer units.
 12. The fluororesin according toclaim 5, wherein the tetrafluoroethylene/perfluoro(alkyl vinyl ether)copolymer has a perfluoro(alkyl vinyl ether) unit content of 1.9 to 4.5mole percent relative to all the monomer units.
 13. The fluororesinaccording to claim 3, which is a fluororesin for electric wireinsulating.
 14. The fluororesin according to claim 5, which is afluororesin for electric wire insulating.
 15. A insulated electric wirecomprising a core wire and a insulating material obtained by insulatingmolding of the fluororesin according to claim 3 for said core wire. 16.A insulated electric wire comprising a core wire and a insulatingmaterial obtained by insulating molding of the fluororesin according toclaim 5 for said core wire.